Substances accompanying vegetable oils, such as for example soybean, rapeseed, sunflower or linseed oil, include phosphatides, proteins, carbohydrates, mucins and colloidal compounds which seriously affect the keeping qualities of the oil and promote hydrolytic and oxidative lipolysis. They interfere with refining because they greatly increase the refining loss. They also have an adverse effect on other operations. For example, they impeded crystallization during fractionation and block the pores of the catalyst during hydrogenation. In the final oil, they would gradually be deposited as a sediment and would thus make it look tainted. For all these reasons, certain oils with a significant content of these substances are degummed. In the present context, degumming means the removal of the entire group of these substance, irrespective of whether or not they are actually mucins. Degumming can be carried out in various ways. For example, the phosphatides can be partly removed by hydration. In this way, they lose their lipophilic character, precipitate from the oil and can be removed. Non-hydratable phospholipids are destroyed with acids and are then removed from the oil by separation. The acid has to be just strong enough to split the phospholipids without attacking the oil. Phosphoric acid or citric acid is mainly used for this purpose. Some oils, such as linseed oil for example, can also be degummed by heat. In this process, which is also known as “breaking the oil”, the starting material is heated to 240 to 280° C. The mucins precipitate and can be removed.
Nevertheless, the lecithin fractions which accumulate during degumming contain valuable raw materials which may be used for other applications in the cosmetic, pharmaceutical and nutrition fields. Thus, the content of various phospholipids in technical lecithin fractions is generally ca. 50 to 55% by weight, sterols and sterol derivatives 1 to 10% by weight, neutral lipids 30 to 40% by weight and ceramides and cerebrosides 0.1 to 0.5% by weight.
However, problems arise from the fact that the quantities of useful products, particularly free sterols and ceramides, are very different and generally small, so that elaborate purification and concentration processes are necessary, but are not economical.
In this connection, various solvent-based processes are known from the prior art for enriching phospholipids from hydratable lecithins, in which acetone is used as an extractant or precipitant. This process is known among experts as deoiling of lecithin. The crude lecithin is extracted with acetone in order to remove the ca. 30–40% neutral lipids. Both powder-form and granulated products with a residual triglyceride content of ca. 1–2% are obtained. The disadvantage is that acetone is expensive to use and the products have only limited purity. Since acetone is a highly untypical solvent in the oil-processing industry, manufacturers of lecithin products were beginning to ask themselves as early as the end of the 80's whether permits to use this solvent would continue to be granted in the future.
Processes for working up degumming residues by ultrafiltration are also known in principle. According to U.S. Pat. No. 4,093,540 (Lever Brothers) and U.S. Pat. No. 6,797,172 (The Texas A&M University System), useful materials can be enriched by subjecting vegetable oil to ultrafiltration through a membrane. In these processes, however, all the oil, not the lecithin, is passed through a membrane. EP 0049914 A1 (Unilever) relates to the purification of lecithin by ultrafiltration. The purification of lecithins by filtration through a semipermeable membrane is also the subject of Japanese patent JP 62-039594 (Rinoru). U.S. Pat. No. 6,140,519 (Archer Daniels) also relates to an ultrafiltration process by which purified phosphatides can be produced. However, none of the processes offers a coherent teaching by which the various useful materials could be economically produced in sufficient yields and purities in a way that would be easy to carry out on an industrial scale.
Processes for fractionating deoiled lecithins are also known. They may be divided into three variants.
In the solvent process, the phosphatide-containing mixtures are dissolved in hexane or acetone and 50% by vol. ethanol is added to the resulting solution. Two phases are formed: the heavier phase mainly contains phosphatidyl inositol/phosphatidyl ethanolamine while the lighter phase essentially contains phosphatidyl choline/phosphatidyl ethanolamine [cf. Bailey's Industrial Oil & Fat Products, Volume 1, Edible Oil & Fat Products; General Applications]. The disadvantage of this process lies in the poor enrichment of a phospholipid component.
Although pure fractions can be obtained by chromatographic separation processes, such as preparative HPLC for example, the production costs are so high that economic operation is not possible.
DD 27546 (Humboldt University, Berlin), WO 83/003620 (Unilever) and EP 0049914 A1 (Unilever) describe processes in which the phospholipids are separated into fractions by membranes, i.e. ultrafiltration, and addition of polar solvents. However, the active-substance content in the fractions is comparatively small; in addition, the production of sterols and sterol derivatives is not considered.
Extraction processes for the production of sterols are also known. U.S. Pat. No. 2,415,313 (Refining Unincorporated Houston) relates to a process for enriching sterols and sterol glycosides in which corresponding vegetable oils are subjected to solvent extraction. However, neither purity nor yields are discussed. According to the teaching of U.S. Pat. No. 2,445,931 (US Secretary of Agriculture), alcohols are added to the vegetable oils to precipitate a solid which is only assumed to contain sterols and lecithins. Finally, a report published in Rev. Franc. Corps Gras 5, pp. 307–315 (1958) relates to the extraction of non-hydratable phosphatides with acetone. However, at 0.3%, the quantities of sterols thus produced are very small. Accordingly, these processes also do not offer any teaching as to how various useful materials can be simultaneously and economically produced from lecithins or lecithin-containing oil mucins.
The working up of sterols from triglyceride-containing mixtures is also known. In the first process variant, the complete mixture is saponified by addition of alkali and extracted with solvent, such as EDCL and/or heptane for example. After concentration, the sterols are obtained by cooling crystallization. In the second process variant, the mixture is transesterified with methanol in a high-pressure stage. The methyl esters obtained are then distilled off until ca. 30% free sterols are present in the residue. The free sterols are then obtained from the methyl ester mixture by cooling crystallization.
Accordingly, the problem addressed by the present invention was simultaneously to recover sterols and polar lipids in high purities from technical lecithin mixtures or lecithin-containing residues from the degumming of vegetable oils with minimal outlay on equipment and under economically acceptable conditions.